Death throes of a massive star burp up 10 Jupiters worth of gas

This shedding of outer layers could allow prediction of some supernovae.

Infrared image of one of the biggest, brightest stars known: the Pistol Star. Known as a luminous blue variable, this type of star ends its life as a supernova. The shedding of mass over a month before the final explosion could allow astronomers to predict when it will take place.

D. F. Figer (UCLA) et al./NICMOS/HST/NASA

Supernovae are some of the brightest events in the entire Universe, outshining whole galaxies at their peak luminosity. However, they are rare events at the level of individual galaxies. Since the progenitors may be relatively dim, they are hard to spot, so monitoring the sky for future explosions is a daunting task. Based on observations, however, at least some stars shed a lot of mass prior to the explosion—an event that could be seen in advance.

Observers monitored one such star beginning 40 days before the explosion. By measuring the energy signature of the ejected matter and the spectrum of the subsequent explosion, E. O. Ofek and colleagues were able to connect the two events, showing they were not merely coincidental. Additionally, by studying the evolution of the system before, during, and after the supernova, the researchers found a coherent explanation for one type of supernova, and a means to spot them before they happen.

Supernovas are broadly divided into two categories: white dwarf supernovae (also known as type Ia) and core-collapse supernovae. The second category occurs in very massive stars (at least 8 times the mass of the Sun) that use up their fuel and explode because their cores can no longer withstand the pressure of their own gravity. Although core collapse supernovae have that in common, their progenitor stars can be quite diverse. The current study focused on type IIn supernovae (sometimes abbreviated as SNIIn), which are widely thought to be explosions of extremely rare stars known as luminous blue variables—some of the most massive and brightest stars known.

SNIIn explosions are characterized by relatively narrow hydrogen emission lines. The width of emission lines are related to the thickness of the gas surrounding the star, and how rapidly that gas is moving. The narrow hydrogen lines distinguishing SNIIn are from relatively thin shrouds of gas, ionized either by the intense radiation or the powerful shock waves produced during the supernova explosion. According to current explanations, this feature can be understood if the dying star shed a lot of mass before the explosion, which then interacted with the matter ejected during the supernova event, producing these emissions.

Supernova SN 2010mc was spotted by the Palomar Transient Factory (PTF), which looks for supernovae and other one-time (transient) events in a wide swath of the sky. As the name suggests, light from SN 2010mc arrived at Earth in 2010. (The first supernova of the year was 2010a; the 27th was 2010aa. Thus, there were a lot before 2010mc, but I'm too lazy to work out what number that was.) Going back in the PTF archives, the researchers discovered a precurser outburst, from the same region of the sky, which occurred 40 days earlier.

Because the non-supernova outburst and SN 2010mc were connected in time and space, it would be extremely unlikely they were coincidental. SN 2010mc was a SNIIn explosion based on its spectrum, so the relatively long period of observation allowed the astronomers to make detailed comparisons of the system's evolution to plausible models. (The research team also identified two other similar supernovae in the PTF data, but their total history was less clear.)

The story of SN 2010mc went like this: decades or even centuries before, a luminous blue variable star shed multiple layers of material into space. These began moving rapidly, but slowed as they interacted with gas in interstellar space. The final outburst before the supernova itself was particularly huge: about 10 Jupiters worth of gas was ejected at about 2,000 kilometers per second.

The supernova debris hit those previous ejected shells with dramatic effect, ionizing the gas and causing distinctive emission lines . However, as the shock front from the supernova expanded, it wiped those spectral lines out. The data even hinted that the whole system brightened again as the more distant ejected shells were engulfed.

Taken as a whole, the events leading up to and following SN 2010mc were consistent with the existing models of SNIIn explosions. As an added bonus, the researchers were able to compare the event to specific models of the precursor, focusing on the way the star shed mass. They concluded that similar supernovae should be predictable, provided we monitor luminous blue variable stars for telltale outbursts.

While these stars are rare, they include the dramatic binary star system Eta Carinae and up to 19 other relatively nearby stars. With a successful prediction scheme in place, we might be able to predict when they will explode with enough time to point our telescopes, prepare our observations, and make popcorn.

mc = 26*13 + 3 = 341. I wonder why this use this instead of decimal numbers. This is still pretty awesome nevertheless.

I can think of at least one reason that may or may not be the historical justification. Supernovae names begin SN#### with digits # representing the year. If you continued to use digits, it'd either be difficult to disentangle the year from the number at a glance (e.g. SN194319), or else you'd need to include a space or dash that would take up more room in catalogues and look more cluttered (SN1943-19). The alternative is switching to letters, for a clear divide between date and number that doesn't require spaces (SN1943s).

mc = 26*13 + 3 = 341. I wonder why this use this instead of decimal numbers. This is still pretty awesome nevertheless.

I can think of at least one reason that may or may not be the historical justification. Supernovae names begin SN#### with digits # representing the year. If you continued to use digits, it'd either be difficult to disentangle the year from the number at a glance (e.g. SN194319), or else you'd need to include a space or dash that would take up more room in catalogues and look more cluttered (SN1943-19). The alternative is switching to letters, for a clear divide between date and number that doesn't require spaces (SN1943s).

I like SN1943-343 better than SN1943me. Even though it is more digits, the dash makes it very easy to read.

mc = 26*13 + 3 = 341. I wonder why this use this instead of decimal numbers. This is still pretty awesome nevertheless.

I can think of at least one reason that may or may not be the historical justification. Supernovae names begin SN#### with digits # representing the year. If you continued to use digits, it'd either be difficult to disentangle the year from the number at a glance (e.g. SN194319), or else you'd need to include a space or dash that would take up more room in catalogues and look more cluttered (SN1943-19). The alternative is switching to letters, for a clear divide between date and number that doesn't require spaces (SN1943s).

I like SN1943-343 better than SN1943me. Even though it is more digits, the dash makes it very easy to read.

Perhaps a more Star Trek oriented convention would be SN1943.343 instead? A clear statement delineation with enough visual spacing for clarity?

Author declares himself to be too lazy to determine a simple math problem on a technical article that includes theories based on advanced math. That's cool, we'll let the community figure it out and argue the correct way to figure it out.

My way was to fire up excel and count across. But I don't have 2010, and LibreOffice is at home. So I gave myself two column a blank first column and the second column was 65..90. I then repeated 65..90 in the second column and 65 in the first column. Then continued down. Third column was =CHAR(A1)&CHAR(B1). Go to the result for MC ... and, it falling on row 341, I had my answer.

I suppose that was more tedious than figuring out the math equation; but, for me, took less brain power.

Also, regarding Eta Carinae, just throwing this thought out there, but it doesn't seem reasonable that the LBV of this binary system would ever collapse under its own gravity as it has a second star also pulling on its mass. Granted, the star has blown out a lot of mass already. And I may be misunderstanding the properties of gravity. So take my thought for what it's worth.

Also, regarding Eta Carinae, just throwing this thought out there, but it doesn't seem reasonable that the LBV of this binary system would ever collapse under its own gravity as it has a second star also pulling on its mass. Granted, the star has blown out a lot of mass already. And I may be misunderstanding the properties of gravity. So take my thought for what it's worth.

You agree that, were the ground not preventing it, Earth's oceans would fall to its center despite being pulled on by the Moon and Sun? In a supernova, the fusion that provided the pressure necessary to support the oceans has stopped (ie, the ground has disappeared but all the mass is still there), and the star falls into the center of gravity. Boom.